Identification of a novel splicing form of zebrafish p73 having a strong transcriptional activity

p73 is a transcriptional activator related to tumor suppressor p53 and regulates differentiation, cell-cycle arrest, and apoptosis. Recently, zebrafish p73 (zp73alpha) was isolated and shown to be required for zebrafish embryogenesis. In this study, we isolated a novel splicing-variant of zp73 mRNA, which was generated by the use of an alternative splicing acceptor site, and designated it as zp73theta;. The zp73theta; mRNA encoded a carboxy-terminal structure distinct from that of zp73alpha. Whereas the expression level of zp73theta; mRNA was much lower than that of zp73alpha in zebrafish adult tissues, it was relatively high and fluctuated during embryogenesis. Using Saos-2 cells for a transient reporter assay, we found that zp73theta;, but not zp73alpha, had strong transcriptional activity when the experiments were performed at 34 degrees C. In addition, zp73theta; had the ability to suppress the growth of Saos-2 cells and to cause the developmental defects in zebrafish. These data indicated that zp73theta; could work as a transcriptional activator in zebrafish.